Many vehicle designs utilize disc brakes and/or drum brakes. For example, typical parking brake configurations continuously employ regular drum brakes on a rear wheel. Parking brakes commonly rely on simple mechanical linkage to engage the brakes. The driver may simply pull a lever which is coupled to a brake cable which actuates the brakes. To release the brake, a button is pressed while lifting and releasing the lever. For these types of parking brakes, there may be a relatively large amount of “play” in the brake cable, i.e., a relatively large range of motion of the lever and brake cable may be required in order to supply sufficient braking force to retain the vehicle in place. This is generally satisfactory, since the drive may simply lift the lever until sufficient force has been applied.
However, in some systems, the parking brake or other brake is engaged electronically. The driver may simply depress a pedal, lever, button or other suitable means, which sends a signal to a controller or actuator which engages the brake.
In these type of systems, since the brake is automatically actuated, it is important to know when a target force is being applied to the wheel(s), such that the vehicle is retained in its current position. Some systems accomplish this by using a force sensor which measure the force being applied by the brake. The brake or brake actuator may therefore be controlled using closed loop forced feedback.
However, such sensors add cost to the system. And harsh environmental factors, such as temperature variation and moisture, reduce the reliability and accuracy of the sensors. Additional circuitry may be used to compensate for the drift and sensitivity variations caused by the factors, however, this again adds cost and complexity to the system.
One system aimed at detecting a contact point of a brake is discloses in U.S. Pat. No. 6,279,694 issued Aug. 28, 2001 to Jürgen Böhm et al. and assigned to ITT Manufacturing Enterprises Inc. The '694 patent discloses a system for adjusting a brake based on sensed position. However, there are two inherent problems with the Böhm system. First, it only detects the contact position during an apply mode. Second, the system returns erroneous results when initiated and the brake is already being applied.
The present invention is aimed at one or more of the problems identified above.